Is there really a need for such PSU for consumers? Haven't seen any popular case after EVGA Hadron.

It's definitely niche. Though there have been a few cases going for smallest form factor possible that have used FlexATX it's definitely niche. The only modern case I have seen was on IndieGoGo (IIRC) but this will definitely open up the gateway for those machines.

Many people said the same thing about SFX when the first Silverstone units dropped as well.